This invention relates to interior space daylighting systems and, in particular, to a mini-optical light shelf daylighting system that redirects incident daylight on to the ceiling plane of an interior space to illuminate the interior space.
It is a problem in the field of interior space illumination to provide a cost effective mode of illumination that makes use of the incident daylight without the need for complex systems or significant occupant intervention. Existing daylighting systems are of limited effectiveness, limited applicability due to their architectural limitations, or require complex and expensive mechanical and electronic control mechanisms. In addition, glare represents a significant problem with existing daylighting systems, since glare, caused by direct sunlight penetrating through or over the daylighting system, or sunlight striking the daylighting system components and being reflected into the interior space, causes visual discomfort.
There is a need for systems that provide improved energy efficiency and environmental quality in buildings. One such example is a system that reduces the consumption of electricity for lighting. One option for reducing electricity consumption for lighting is to use daylight to illuminate occupied building spaces during daylight hours. These systems are termed xe2x80x9cdaylighting systems.xe2x80x9d The key to the widespread use of daylighting systems is the provision of such a system that is both inexpensive and easily applied to both new and existing buildings. In addition to the savings attributed to reduced electricity consumption, daylighting systems typically also result in increased productivity by the occupants of the illuminated space, reduced health problems evidenced by the occupants of the illuminated space, and pollution reduction. This is because there appears to be a strong correlation between the quality of the luminous environment and exposure to daylight and the overall health and productivity of the occupants.
One such existing daylighting system is the traditional interior light shelf, which comprises an optical device which receives daylight that is transmitted through a window and redirects it onto the interior ceiling plane, thereby creating a useful source of interior illumination. The basic light shelf concept typically comprises a wide flat elongated interior light shelf located adjacent to a window and protruding into a room from the exterior wall of a building, and/or an exterior light shelf of weather-resistant construction projecting from the exterior wall of the building, coplanar with the interior light shelf to receive incident daylight. The incident daylight is reflected by the interior and/or exterior surfaces onto the ceiling of the occupied space by a diffuse or specular horizontal or slightly sloped surface of the light shelf, which light reflecting surface is located above a view glazing. However, the interior light shelf typically protrudes a significant distance into the occupied space and is problematic from architectural, visual comfort, mechanical and aesthetic standpoints in many room applications.
Another existing system is disclosed in PCT published application WO 91/03682 which discloses an illuminating apparatus comprising a plurality of solid illuminating channels, manufactured from a transparent material, that are adhesively bonded together to form cavities in the illuminating apparatus. The cavities create a single smooth light reflecting surface on the bottom surface of each illuminating channel and two interconnected light reflecting surfaces on the top surface of each illuminating channel. Incident light is either reflected directly off the single smooth light reflecting surface on the bottom surface of an illuminating channel or total internal reflection off the opposite surfaces of the illuminating channel. The total internal reflection consists of incident light reflecting in turn off a first of the two interconnected light reflecting surfaces on the top surface of an illuminating channel, the single smooth light reflecting surface on the bottom surface of the illuminating channel, then the second of the two interconnected light reflecting surfaces on the top surface of the illuminating channel. This illuminating apparatus is costly and heavy due to the use of plurality of solid illuminating channels, manufactured from a transparent material, that are adhesively bonded together. The need for the use of solid material to form the illuminating channels is due to the need to implement total internal reflection to redirect a portion of the incident light.
The above-noted U.S. patent application Ser. No. 09/249,664, titled xe2x80x9cMini-Optical Light Shelf Daylighting System,xe2x80x9d filed on Feb. 2, 2001 and U.S. Pat. No. 6,239,910 B1, titled xe2x80x9cMini-Optical Light Shelf Daylighting Systemxe2x80x9d represent significant advances in the field of daylighting systems. These systems are implemented in the paradigm of a window treatment positioned adjacent to the interior surface of the window glazing and located above the normal occupant viewing height. These daylighting systems redirect the incident daylight that arrives through the window glazing of the building from a range of directions and altitude angles into a limited spread of light onto the ceiling of the interior space of the room. The light redirecting elements used in these systems have a unique geometry which consists of 3 adjoining arcs with descending radii forming a slat having a specular top optical surface. This unique geometry of the light slats optimally redirects light upwards without light striking the bottom surface of the adjacent light shelf thereby preventing glare in the ordinary field of view. A light blocking feature, comprising a segment that is integral to light reflecting surface and extending therefrom at a predetermined location toward the window glazing, forms an acute angle with the light reflecting surface and serves to create a cut-off angle of 15xc2x0. While these systems represent a significant advance over the known daylighting systems, the amount of the incident daylight blocked by these systems reduces their daylighting efficiency.
The above-described problems are solved and a technical advance achieved the field by the present Mini-Optical Light Shelf daylighting system (termed xe2x80x9cMOLS daylighting systemxe2x80x9d herein). The MOLS daylighting system is a passive, static optical device that is typically mounted in a window opening of a building. The MOLS daylighting system receives daylight transmitted through the window opening and efficiently redirects it uniformly onto the interior ceiling plane of a room (or other interior space) in a diffuse manner, thereby creating a useful source of interior illumination.
The MOLS daylighting system comprises multiple light slats, each of which allows light to be efficiently collected and accurately directed onto the ceiling plane of a room, while at the same time shading the occupants of the room from direct daylight penetration through the light slats at angles above 5xc2x0. The light slats are narrow and can be implemented in the paradigm of an insert located between adjacent panes of the glazing or in a mini-blind window treatment. The window area is typically partitioned into a view related glazing section and a daylight collection and redirection glazing section. The occupant""s views out of the building remain unobstructed through the view related section of the glazing to a height of approximately seven feet above the floor. Traditional window treatments can be used for this portion of the glazing for shading, privacy, and blackout control.
Each light slat consists of a light reflecting segment that comprises the top surface of the light slat. A light shading segment and a light redirecting segment comprise the bottom surface of the light slat. The daylight incident on the daylight collection section of the glazing is collected by the optically shaped light reflecting segment of the light slats and redirected onto the ceiling plane of the room in a glare free, uniform manner. In addition, the light redirecting segment of each light slat functions to redirect incident daylight, that is reflected off the light reflecting segment of the adjacent light slat at angles above a predetermined threshold, onto the ceiling plane of the room in a glare free, uniform manner. The light shading segment functions to block low altitude components of incident daylight from entering the room between adjacent slats.
The MOLS daylighting system produces effective daylighting for typical ambient light levels for the perimeter zones of a building, and can effectively operate for room depths in excess of 35 feet deep, depending on the vertical height of the window and the particular implementation of the MOLS daylighting system. The optical geometries of the light slats and the associated reflective surface characteristics cooperatively diffuse the collected daylight uniformly across the ceiling plane of the room. The resultant indirect lighting is striation free and substantially uniform in illuminance. The use of daylight preserves the visual and psychological connection between the occupants and the outdoors due to the subtle color and illuminance changes which occur throughout the day. Visual comfort is enhanced by evenly diffusing the daylight across the ceiling plane of the room from the perimeter wall to the interior extent of the illumination and by minimizing any downward directed rays.